Two component partially removable electrophotographic developer powder and process for utilizing same



3,236,639 TWO CGMPQNENT PARTIALLY REMOVABLE ELECTROPHOTOGRAPHIC DEVELOPER POW- DER AND PROCESS FOR UTILIZING SAME Martha Tomanek, ne Kunitzer, Wiesbaden-Biehrich, Germany, assignor, by ruesne assignments, to Azoplate Corporation, Murray Hill, NJ.

No Drawing. Filed Aug. 18, 1960, Ser. No. 50,316 Claims priority, application Germany, Sept. 4, 1959, K 38,623 32. Claims. (Cl. 961) The preparation of images by electrophotographic processes is known. In these processes, a coating on a support is provided, in the absence of light, with an electrostatic charge. The material is exposed under a master to light by the contact process, or an image is projected thereon by means of an optical system, whereupon an electrostatic image corresponding to the master is produced. This image is developed by being briefly contacted with a developer consisting of a toner and a carrier, whereupon the toner adheres to the image parts. The image is then fixed by heating. When a suitable support is used, the image-free portions may then be rendered hydrophilic by treatment with an alkaline liquid, while the image portions covered by the hydrophobic toner are inked up with greasy ink. A printing plate prepared in this manner is suitable for planographic printing.

In the mixture of carrier and toner hitherto used for the development of the electrostatic image, particles were used for the carrier which were 10 to 100 times larger and of greater specific gravity than the toner particles, e.g., particles with a diameter of from 0.2 to 0.6 mm. Owing to their size, the gravity forces acting on the carrier particles exceed the attraction by the charged portions of the photoconductive layer, so that the carrier particles do not adhere to the layer.

Materials that have been used as toners are pigmented or non-pigmented thermoplastic or fusible electroscopic resin powders.

When the developer is in use, the toner acquires, as a result of frictional electricity, a charge of the opposite polarity to that of the carrier material. Thus, the fine resin powder is loosely held by the carrier material so that the two components do not separate out. When the developer is scattered over the electrostatic image, the toner particles are attracted to the image that is being developed, if this has a charge of the opposite polarity to that of the toner, while the carrier particles roll away. Thus, according to the polarity of the toner contained in the developer, or of the electrostatic image, either the image portions or the image-free portions of the electrophotographic material are covered during the development process.

The known developers, consisting of coarse carrier particles and fine toner particles, have the disadvantage that the outlines of the developed image do not always have the desired degree of sharpness.

A developer for electrophotographic purposes has now been found which consists of one or more toners which acquire a positive charge and one or more toners which acquire a negative charge, the toners being of approximately equal grain size and those of at least one polarity being soluble in water, alkalis or acids, or decomposing when heated to give volatile substances or substances which are readily soluble in these media.

The developer of the invention thus consists of two or more toners of approximately equal grain size, of which the toner or toners of one polarity can be removed after the fixing process by being dissolved in water, alkalis or acids, or of which the toners of one polarity can be converted by heat during the fixing process into highly volanited States Patent ice tile products or into products which are readily soluble in water, alkalis or acids and thereby are removed.

Mixtures in which the toners of one polarity can be removed in one way, e.g., by dissolving in alkalis, and the toners of the other polarity can be removed by one of the other methods, e.g., by dissolving in acids or by heating, also are within the invention.

For the preparation of the developers, toners which acquire a negative charge, or alternatively toners which acquire a positive charge, are combined with those which can be removed after the fixing process in the stated manner, or a number of the removable toners are mixed with each other.

Materials suitable as positive toners for the developers of the invention include natural and synthetic resins, such as colophony, copals, dammar resin, asphalts, colophonymodified resins, ketone resins, maleic resins, coumarone resin, polyacrylic acid resins, and polystyrenes. Also mixtures of these resins can be used. Inorganic and/or organic pigments and/or dyestuffs are added to these resins to impart a definite positive polarity thereto. Suitable materials include carbon black, zinc oxide, titanium dioxide, barium sulfate, red lead and the following dyestufis from Schultz Farbstofitabellen, vol. 1, 7th edition (1931) Helio Red RMT (No. 200), Helio Fast Blue (No. 1188), Sudan dyestuffs, e.g., I (No. 33), II (No. 92), HI (No. 532), CB (No. 127), R (No. 149), Cellitone dyestuffs (Colour Index, vol. 1, 2nd edition, 1956, p. 1655-1742), Spirit-soluble Nigrosine (No. 985) Pigment Black B (No. 1361), Alizarin Blue Black B (No. 1195), Diamond Black F (No. 614), Fanal Violet LB (No. 803) and also mixtures of such dyestuffs and/ or pigments. Often, small quantities of these substances sufiice, e.g., 0.5% by weight of carbon black, to impart a definite positive character to the resins. Further, it is often advantageous for small quantities, e.g., 0.1 to 10%, preferably 1 t0 5% of waxes and/ or organic compounds of low melting point, and substitution products thereof, to be added to the positive toners to exert a favorable eifect on the melting point and the adhesive power of the toner mixture.

Waxes suitable for this purpose include natural waxes, such as carnauba wax, beeswax, Japan wax, montan wax and ceresin, and synthetic waxes such as those available under the trade names A-Wachs, OP-Wachs, SPO- Wachs, V-Wachs, O-Wachs, E-Wachs, Hartwachs H, Hartwachs W, various of those known as Ruhr Waxes and in particular, the products commercially available under the name Gersthofener Wachse with the codings S, L, O and OF.

The organic compounds of low melting point that are of particular interest are substituted and unsubstituted aromatic compounds with a melting point between about 40 and 150 C.

Such compounds, include naphthols, e.g., 1-naphthol and Z-naphthol, and also aromatic compounds such as acenaphthene, acylamino compounds, e.g., acetanilide, halogenated aromatic compounds such as pdibromoben zene, amino compounds such as 2,4-dia'minotoluene and o-phenylene diamine, phenols such as resorcinol, and diphenylamine and derivatives thereof.

For the negatively charged toners, metal resinates are particularly suitable. Metal resinates, also known as resin soaps, are salts, of the metals of the first to the eighth group of the Periodic System, of resin acids.

In the present case metal resinates, and mixtures thereof, of metals such as aluminum, barium, lead, calcium, cerium, iron, cobalt, copper, magnesium, manganese and zinc are particularly of interest.

In addition to these metal resinates, resins of the types that may be used for the preparation of the positive toners may be added to the negative toners in quantities of up to 50% by weight. Similarly, proportions of the waxes and organic compounds mentioned above of low melting point i.e., between about 40 and 150 C., may also be added to the metal resinates. As dyestuffs and pigments, those described in conjunction with the positive toners may be used. However, in general, the content of pigments and dyestuffs should not exceed 10% of the metal resinates, if negative polarity is to be adequately maintained.

If, however, dyestuffs containing metals are used, quantities of up to about 50% by weight but preferably not more than 35%, may be added.

As dyestuffs containing metals, those may be mentioned which contain metals such as copper, zinc, magnesium, iron, sodium or potassium, contained in the molecule in complex form. Complexes such as chlorophyll or copper-zinc or magnesium phthalocyanines or Naphthol Green B are of such nature.

Also, double salts of dyestuff molecules, e.g., zinc chloride double salts of the following: (the numbers given are those under which the dyestuffs are listed in Schultz, Farbstolftabellen, vol. 1, 7th edition (1931)): Toluidine Blue (No. 1041), Methylene Green B (No. 1040) or Acridine Orange 2G (No. 902) may be used. Other possibilities include complexes of heteropoly acids, e.g., phospho-molybdotungstenic acid, with dyestuffs, e.g., the substances known as Fanal dyestuffs, e.g., Fanal Red 6 B (ibid, No. 864), Fanal Violet LB (ibid., No. 803), Fanal Blue B (ibid., No. 822). Metal salts of sulfonic and carboxylic acids of dyestuffs, e.g., Alizarin Blue-Black B (ibid., No. 1195), and Diamond Black F (ibid., No. 614) are also of interest.

For the preparation of the toners, the pulverized starting materials are advantageously ground together very finely; the mixture is heated to melting temperature and stirred until a highly homogeneous state is achieved, after which the melt is cooled. The fusible starting materials may on the other hand be liquified by heating and the other components then added, with stirring, after which the mixture is cooled. The toner mass thus obtained is finely ground and then sieved. Sieve fractions with an average particle size of about 1 to 100p, preferably about to 30,11. are used for the toner.

Substances that may be used as alkali-soluble toners include sulfonic acids and, in particular, carboxylic acids such as oxalic acid, adipic acid, tartaric acid, benzoic acid, aminobenzoic acid, chloro-benzoic acid, naphthalic acid, 2-hydroxy-1-naphthoic acid, tetrachlorophthalic acid, anthraquinonecarboxylic acid, benzenesulfonic acid, chlorobenzenesulfonic acid, naphthalenesulfonic acid, naphthalsulfonic acid, naphthylamine sulfonic acids, aminonaphtholsulfonic acids, benzidinesulfonic acids, anthracenesulfonic acids, and anthraquinonesulfonic acids. Also, acid anhydrides, such as naphthalic anhydride, phthalic anhydride, tetrachlorophthalic anhydride and acid imides such as naphthalic acid imide, hydroxynaphthalic acid imide, perylene-3,4,9,IO-tetracarboxylic acid diimide, sulfonamides, such as toluene-sulfonamide, naphthalene-sulfonamide, naphthalene-sulfonanilide, anthracene-l-sulfonanilide, S-(p-toluenesulfonamido)-acenaphthene, phenylsulfanilide, imidazoles such as benzimidazole, 2-methylbenzimidazole, 6-chloro-Z-methyl-benzimidazole, 2-(4-diethylaminophenyD-benzimidazole, Z-mercaptobenzimidazole, 2-phenylphenanthro-9, :4,5-imidazole, 2-(4-aminophenyl) 4,5-diphenyl-imidazole, 2 styryl 6- (or 5-)- amino benzimidazole, naphthimidazole l, 2:4,5, 2- methyl-S- (or 6-) -nitro-benzimidazole, hydroxy compounds such as resorcinol, 4-hydroXy-diphenyl, 4-hydroxybenzophenone, naphthols such as l-naphthol, 1-chloro-2- napht-hol, purpurogallin, pyrogallol, 2,3-dihydroxy-naphthalene, phloroglucinol, S-hydroxy acenaplrthene, 1,2,3- trihydroxy-anthraquinone, triazole compounds such as 2,5 diphenyl-1,3,4-triazole, pyrazole compounds such as 3,5- diphenyl-pyrazole and 3-(p-methoxyphenyl)-5-phenylpyrazole may be used. The alkali-soluble organic compounds may be uncolored or they may be colored with organic dyestuffs or organic or inorganic pigments. As dyestuffs and pigments the same compounds may be used which are described for coloring of positively as also for negatively charged toners. The preparation also is the same.

Resins obtained by the polymerization of vinyl chloride with esters of fatty acids such as acetic acid, propionic acid and butyric acid and also containing a certain proportion of unsaturated monocarboxylic acids such as crotonic acid, and cinnamic acid or unsaturated dicarboxylic acids, such as maleic acid, fumaric acid or itaconic acid are also very suitable as alkali-soluble toners. Products of this type are commercially available. Also, styrene/maleic acid interpolymers and resins having a high acid number, e.g. over 150, are useful. Such resins include those of which colophony forms the major parts, e.g., a resin with a melting point between and 107 C., and an acid number between 210 and 240 (Laropal S), maleinate resins, e.g., a product with a melting point of -130 C. and an acid number of 270 to 300 (Arochem 404), oil-free alkyl resins, e.g., a product with a melting point of 7793 C., and an acid number of 180200 (Phthalopal PP), or a melting point of 66 to 70 C., and an acid number of 180 to 200 (Alphthalat), and also processed natural resins such as a product with a melting point of 110/95 C. (Kofier Bank) and an acid number of 160 to 150 (Erkazit- Spritharz Materials which may be used as acid-soluble toners include solid basic organic compounds such as phenylenediamine, benzidine, diphenylamine, naphthylamine, naphthylenediamine, 5,6-benzoquinoline, 5,6 benzoquin-oline, 5,6-benzoquinaldine, 4-chloraniline, 4,4'-diaminobenzophenone and the triazole, imidazole and pyrazole compounds mentioned above among the alkali-soluble compounds which, as a result of the presence of an NH group, are also acid-soluble.

Materials which may be used as water-soluble toners include salts of the alkali-soluble toners, particularly the alkali metal salts thereof and also the salts of the acidsoluble toners, particularly with strong inorganic acids.

Exemplary are alkali metal salts of organic aliphatic, aromatic or heterocy-clic carboxylic acids or sulfonic acids such as sodium acetate, lithium citrate, sodiumpotassium tartrate, sodium benzoate, the sodium salt of naphthalene-l-carboxylic acid, the disodium salt of naphthalene-1,5-disulfonic acid, the potassium salt of anthracene-l-sulfonic acid, the potassium salt of fluorene dicarboxylic acid, the sodium salt of l-phenyl-S- methylpyrazole-carboxylic acid, water-soluble sulfonimides such as benzoic acid sulfimide, and dibenzene sulfonylimide. Also, lower watersoluble organic carboxylic acids, diand tricarboxylic acids and hydroxycarboxylic acids, such as oxalic acid, succinic acid, adipic acid, maleic acid, tartaric acid, malic acid, citric acid, salicylic acid, and resorcylic acid and water-soluble resins such as polyvinyl alcohols, polyvinyl pyrrolidones and condensed melamine-formaldehyde resins of lower molecular weight are included.

Compounds which may be used for toners that decompose under the influence of heat include, in particular, readily decomposable carboxylic acids such as malonic acid, acetone dicarboxylic acid, citraconic acid and furfural malonic acid.

For the preparation of the developers of the invention, the toners which acquire a negative charge and those which acquire a positive charge are mixed together in proportions of 1:1 to 20:1. Preferably, approximately equal proportions of the twotypes of toner are used.

The developers of the invention are applied in known manner to the electrostatic images to be developed and are then fixed, preferably by heating. It is also possible for the toner to be irremovably anchored to the photoconductor coating by the use, particularly in the form of vapor, of solvents for the toner or for the photoconductor coating in question. Also, the developed electrostatic image may, before being fixed, be transferred to another material, more particularly with the assistance of a corona discharge, and then fixed on the transfer material.

In this case, the transfer material, e.g., a sheet of paper, is placed onto the unfixed powder image and charged with a corona discharge having the same polarity as the original charge of the now developed electrostatic image, so that the powder image is attracted by the paper and may then be fixed thereon, e. g., by heating.

Toner particles then adhere both to the image portions and to the image-free portions or, alternatively if a toner that decomposes under the influence of heat is used, the toner will be removed, during the heating process, either in the image portions or in the image-free portions, according to the polarity of the electrostatic image. The developers according to the present invention are of particular advantage in those cases where really fine lines or screen dots are to be reproduced, e.g., for the preparation of printing plates.

For conversion into printing surfaces, the developed electrostatic images are wiped over with acid or alkaline agents so that the photoconductor coating, and where necessary the toner coating, are removed and the support is bared in the portions that are to be made waterconductive. Thus, for the photoconductor coatings, compounds are advantageously used which are soluble in acids or alkalis.

In the preparation of the printing plates, the solubility characteristics of the toner are selected according to the photoconductor coating used and the polartiy of the charge applied, so that either direct images or direct reversed images are obtained. It is, for example, an advantage for the developer to be prepared from one toner which is soluble in acids and one which is soluble in alkalis. As the photoconductor coating may be charged either positively or negatively, it is possible, simply by suitable choice of polarity, for the toner particles, with solubility characteristics corresponding to those of the photoconductor coating, to be deposited either in the image-free portions or in the image portions, according to whether a direct or reversed form of the master is to be prepared as a printing plate.

If, for example, the electrophotographic material has a photoconductor coating which is soluble 1n alkalls and the developer has a toner, soluble in alkalis, as the one which acquires a positive charge and if the photo conductor coating is then negatively charged, a printing plate will be obtained, after the developing and fixing processes and the alkaline treatment, which presents a reversed image of the master. If direct images are required, then the coating will be given a positive charge; in other respects the procedure is the same. If, in the same developer, an acid-soluble toner is used as the one which acquires a negative charge, this can also be used for electrophotographic material the photoconductor coating of which is soluble in acids. Thus, with negative charging, direct images are obtained and with positive charging revised images.

After the electrophotographic image has been developed and fixed, it is converted into a printing surface by treatment with an alkaline or an acid liquid, according to the solubility characteristics of the photoconductor coating. By this means, in the portions that are to be made water-conductive, either the image or the image-free portions of the photo-conductor coating, according to the nature of the development, are dissolved away together with any toner, or decomposition products thereof, present thereon; the supporting material is bared and thereby, or by a special further treatment, made hydrophilic. The treatment takes the form of a simple wiping-over process, e.g. by means of a cotton pad. Alternatively, the plate may be immersed in the developing bath or suitable mechanical devices may be used by which the liquid can be applied, e.g., rollers.

The electrophotographic material used is preferably that having organic photoconductor coatings on a support, preferably metal and particularly aluminum.

The base materials used as supports may be any that satisfy the requirements of electrophotography, e.g., metal or glass plates, paper or plates or foils made of electroconductive resins or plastics, such as polyvinyl alcohol, polyamides, and polyurethanes. Other plastics which have the required electroconductivity, such as cellulose acetate and cellulose butyrate, especially in a partially saponified form, polyesters, polycarbonates, and polyolefines, if they are covered with an electroconductive layer or if they are coverted into electroconductive materials, e.g., by chemical treatment with or by introduction of materials which render them electrically conductive, may also be used. Generally speaking, electroconductive supports are suitable for purposes of the present invention. In the sense of the present invention, the term electroconductive support comprises materials having a specific conductivity higher than 1O" ohm* .cm preferably higher than l0 ohm .cm

Examples of organic photoconductors which may be used are: oxadiazoles such as 2,5-bis-(4-dimethylaminophenyl-(1)-1,3,4-oxadiazole, imidazolones such as 4,5 -bis- (4-aminophenyl)-imidazolone-2, triazoles such as 2,5- bis-(4-acetylaminophenyl-(1)) 1,3,4 triazole and pyrazoles such as 1,3,5-triphenylpyrazole.

These are preferably applied to the supporting material in association with a binder and a sensitizer. In the case of the alkali-soluble photoconductor coatings, a resin is used which is soluble in alkalis, e.g., an interpolymer of styrene and maleic anhydride in equal molecular proportions, or other resins having acid groups, e.g., polystyrene sulfonic acid or alkali-soluble phthalic acid ester resins. The photoconductor and the alkali-soluble resin are mixed in proportions of from :10 to 10:90, preferably from 60:40 to 40:60. As liquids for the alkaline treatment, the following may be employed: inorganic and organic alkaline substances such as alkali metal hydroxides, aqueous ammonia, alkaline earth metal hydroxides, alkali metal phosphates, alkali metal polyphosphates and organic primary, secondary and tertiary lower saturated aliphatic and cyclic amines such as trimethylamine, piperidine and also amino alcohols such as triethanolamine.

It can be advantageous for Water-soluble silicates such as sodium silicate, potassium silicate or mixed silicates such as sodium-potassium silicate, which may also contain small quantities of calcium silicate, to be added to the alkaline liquids to improve the hydrophilic properties of the image-free, non-printing portions.

For the preparation of the acid-soluble photoconductor coatings, photoconductors are used which are soluble in acids, e.g., compounds containing NH or NH groups, such as 2,5-bis-(4'-diethylaminophenyl (1')) 1,3,4-triazole, 4- 4'-dimethyl-amino-phenyl -5- (4"-chlorphenyl imidazole, 3-amino-carbazole, l-amino-anthracene, 3-amino-pyrene, and 3,6-diamino-carbazole. These photoconductors, or even photoconduct-ors that are not soluble in acids, may be used in association with acid-soluble resins, preferably in the proportions given above.

As liquids for the acid treatment, acids are used which impart hydrophilic properties to the metal supporting material, e.g., strong inorganic acids, in particular phosphoric acid.

Thickening agents such as cellulose alkyl ether, polyvlnyl alcohol or carbalkoxy celluloses may be added both to the acids and to the liquids used for the alkaline treatment,

It is also possible for the entire image surface of the dc veloped and fixed electrophotographic image to be treated, before the treatment with acids or alkalis, with a lacquer which, during the subsequent treatment, is retained in the image portions while it is dissolved away in the imagefree portions together with the treating solution, the toner and the photoconductor coating. For this purpose, lacquers which contain, in addition to dyestuffs and solvents such as cyclohexane, butyl acetate, tetralin and mineral oils, resins of high molecular weight, such as polyvinyl chloride, polyvinyl acetate, phthalic acid ester resin, maleinate resin and the phenol-formaldehyde resins known as novolaks, have proved satisfactory.

If it is desired to use this lacquering process, it is also possible for a developing powder to be used for the electrostatic image wherein the two differently charged toners are both soluble in alkalis, the one readily and the other less readily. For example, a toner of high molecular weight may be used, consisting of an interpolymer of vinyl chloride with a vinyl ester such as vinyl acetate, and having, also polymerized therein, small proportions of a monoor dicarboxylic acid, such as crotonic acid or maleic acid.

This resin of high molecular weight is relatively insoluble in alkalis, and it is used in association with a toner of low molecular weight which is readily soluble, e.g., 4-amino-anisole-2-sulfonic acid. After the image has been developed, fixed, and then lacquered over with the lacquer described above, it can be converted into a printing surface by treatment with an alkaline developer, e.g., monoethanolamine, the portions bearing the 4-aminoanisole-2sulfonic acid thus being dissolved away.

An analogous procedure can be followed with two different toners which are both soluble in acids.

After the treatment with acid or alkaline liquid, the printing plate is rinsed down with water and inked up with greasy ink. When these printing plates are set up in a printing machine, long runs of prints can be made therefrom.

With the developers of the invention, both the charged and the uncharged portions are covered with toner during development; as a result really fine, sharp contours are obtained so that it is possible for fine-line screens to be prepared.

By the use of a toner mixture, of which at least one toner is readily removed either after or during the fixing process, it is possible for this effect to be exploited in particular in the case of printing forms. Further, it is possible for two toners with fairly widely differing softening or melting points to be used, e.g., with differences in melting point of from 20 to 200 C., preferably from 50 to 150 C. If the toner of higher melting point is used as the one which is removed, this prevents spreading of the contours of the toner of low melting point, so that further improvement in the sharpness of the printing plates is achieved.

The developers described above are advantageously used in the development of printing plates in which one toner is removed together with a part of the coating. However, it is possible, particularly if one toner is colorless, for any other type of electrostatic image to be developed herewith. It is immaterial how the electrostatic image has been produced, e.g., by the action of visible light, X-rays, ultraviolet or infra-red light on coatings of corresponding sensitivity or by direct electronic production of the image on an insulating layer or by transfer of an electrostatic image to an insulating layer.

The invention will be further illustrated by reference to the following specific examples:

Example 1 A foil consisting of bright, rolled aluminum that has been cleaned with trichloroethylene is coated with a mixture consisting of 30 parts by volume of ethylene glycolmonomethyl ether and 1 part by weight of 2,4-bis-(4- diethylaminophenyl(1') )-1,3,4-oxadiazole and 0.8 part by weight of a styrene/maleic anhydride interpolymer with a specific gravity of 1.26-1.28 and a decomposition temperature of 200-240" C.; it is then dried. For the preparation of images on the electrocopying material thus obtained, the coating is negatively charged by a corona discharge and then exposed under a master for one second to the light of a -watt high-pressure mercury vapor lamp. The electrostatic image of the master thus formed is treated with a mixture consisting of (a) 10 parts by weight of a colorless interpolymer in powder form con sisting of 85% vinyl chloride, 14% vinyl acetate and 1% maleic acid, and (b) 3 parts by weight of a toner obtained by melting together, grinding and screening 3 parts by weight of a polystyrene of low melting point (Polystyrol LG), 3 parts by weight of a maleinate resin (e.g., Hobimal P 59), 0.3 part by weight of spirit-soluble Nigrosine and 0.1 part by weight of Pigment Deep Black. The two toners, (a) and (b), have a particle size of about 10 to 20 When mixed they acquire charges of opposite polarity, (a) having a negative charge and (b) a positive. When this developer is scattered over the electrostatic image, the black-pigmented positively charged toner is attracted to the negatively charged image and the colorless negative toner is repelled. The latter is, consequently, retained at the uncharged margins of the black image. The toner image is fixed by heating to about 160 C. For conversion to a printing surface, the image is wiped over with a solution consisting of 10% of monoethanolamine, 5% of sodium silicate and 85% of polyethylene glycol. This alkaline solution dissolves away the imagefree areas of the coating and also the alkali-soluble toner consisting of the vinylchloride/vinyl acetate/maleic acid interpolymer, mentioned above, adhering to the margins of the image. After brief rinsing with water, the plate is inked up with greasy ink and used for printing in an offset machine.

Example 2 The procedure described in Example 1 is followed, but for the development of the electrostatic image, 10 parts by weight of finely pulverized 5-chloro-2-methylbenzimidazole of a particle size of about 20,44 and 10 parts by weight of a mixture consisting of 4 parts by weight of polystyrene, 3 parts by weight of colophony, 2 parts by weight of carbon black and 1 part by weight of spiritsoluble Nigrosine are used. For the preparation of the toner, the resin/dyestuff mixture is melted and the cooled melt is ground and screened. A fraction with a particle size of about 10 to 20a is used for the toner. When the electrostatic image is developed, the toner consisting of the colored polystyrene/colophony mixture adheres to the negatively charged image portions because, when shaken up with 5-chloro-2-methyl-benzimidazole it acquires a positive charge; the 5-chloro 2 methyl-benzimidazole settles on the exposed portions. After the toner image has been fixed with trichloroethylene vapor, the image is converted into a printing plate by wiping over with a solution containing 0.5% monoethanolamine, 60% glycerine and 39.5% ethylene glycol. 5-chloro-2-methylbenzimidazole is dissolved away with the coating. After the plate has been rinsed down with water, it is inked up with greasy ink.

Example 3 30 parts by weight of 2,5-bis-(4-diethylaminophenyl- (1))-1,3,4-triazole and 0.025 part by weight of Rhodamine B Extra are dissolved in a mixture of parts by volume of ethylglyeol monomethylether and 150 parts by volume of toluene. This solution is coated in known manner upon a mechanically roughened aluminum foil and dried. The electrocopying material thus prepared is negatively charged by a corona discharge. A leica positive is then projected, in a photographic enlarging apparatus with an illumination strength of 3 lux, upon the charged electrocopying material, an exposure of one minute being used. Development is then effected with a developer consisting of 10 parts by weight of a finely pulverized benzidine and 2 parts by weight of a colored ketone resin (Kunstharz EM). For the preparation of the colored resin toner, 10 parts by weight of the resin are first melted, 2 parts by weight of carbon black are added, and the mixture is stirred. The cooled melt is ground and sieved. The benzidine and the ketone resin, colored with carbon black, are used in particle sizes of 1030p.. When they are mixed, the benzidine acquires a negative charge and the colored ketone resin a positive charge.

When the electrostatic image is developed, the positively charged toner is attracted to the negatively charged image and the negatively charged toner settles on the non-charged parts. After the image has been fixed, by heating to 130 to 150 C., it is converted into a printing surface by wiping over with a 3% aqueous phosphoric acid solution, to which 5% of gum arabic has been added, and inking up with greasy ink.

Example 4 The procedure described in Example 1 is followed, but the negatively charged coating is exposed to light under a negative master and the electrostatic image is developed with a toner mixture consisting of parts by weight of a finely pulverized 4-amino-anisole-2-sulfonic acid (particle size: 1 to 10 and 10 parts by weight of a colored interpolymer consisting of 85% vinyl chloride, 14% vinyl acetate and 1% maleic acid. When the two toners are mixed, the 4-amino-anisole-Z-sulfonic acid becomes positively charged and the interpolymer negatively charged. 4-amino-anisole-Z-sulfonic acid settles on the unexposed parts, which have a negative charge, and the colored interpolymer on the exposed parts. For the conversion to a printing plate, as both components are alkali-soluble, the entire image side of the foil is treated with a lacquer. The lacquer consists of 11.5 parts by volume of amyl acetate, 25 parts by volume of paraffin oil, 3.5 parts by volume of cyclohexane, 10 parts by weight of a dry alkyd resin, with a castor oil base, and an acid number of 10, and 1.5 parts by weight of a pigment dyestulf with the trade name Sudanrot BK. After the lacquer has dried, it is wiped over with a solution containing 94.5% ethylene glycol, 0.5% monoethanolamine and 5% sodium metasilicate, until the coating is dissolved away in the portions where there is no interpolymer adhering. The 4-amino-anisole-2-sulfonic acid is dissolved away at the same time, while the interpolymer is protected by the lacquer coating. A positive printing plate is obtained from the negative master; after the plate has been inked up with greasy ink it can be used for printing in the usual manner. In order that the image may be made visible before lacquering, the interpolymer may be colored in the following manner: 1 part by weight of a black dispersion dyestuif (Cellitonechtscharz BTNU) is suspended, at 55C., in 1500 parts by Weight of water. 5 parts by weight of phenyl-ethylurethane are added as a carrier and the suspension is cooled at 40 C. with stirring. 50 parts by weight of the interpolymer in powder form are then added in small increments to the suspension, which is kept cooled to 40 C., and stirring is continued for half an hour at 40 C. The temperature is then gradually raised, over the course of 1.5 hours, to 65 C. and stirring is continued for 1 hour at this temperature. The colored powder is separated by suction filtration, washed with water and dried in air. The colored material is ground, to remove any lumps formed during suction filtration, and is then screened. Screened fractions of 1 to 10p. are used for the toner.

Example 5 An aluminum plate coated with selenium is positively charged by a corona discharge and exposed to light under a master. For the development of the electrostatic image, a mixture consisting of 5 parts by weight of zinc resinate (Erkazit-Zinkharz 165) and 5 parts by weight of p-amino-benzoic acid is used. In this mixture,

the zinc resinate is negatively charged and is, therefore, deposited on the unexposed parts bearing the positive charge. The p-amino-benzoic acid is positively charged and adheres to the portions which have been struck by light. A mirror image corresponding to the master is obtained. 'For transfer to a commercially available paper printing foil, the developed electrostatic image is covered with the printing foil, which is then exposed to a corona discharge. The toner is then transferred to the printing foil as a correct image.

After the material has been heated to 150 C., the toners adhere firmly to the surface of the paper. For conversion to a printing surface, the image is wiped over with a solution, consisting of 25% of diethanolamine and of polyethylene glycol, and is inked up with greasy ink.

Example 6 The procedure is as in Example 1 but, for the development, a mixture of two toners is used of which one is obtained from 10 parts by weight of a maleinate resin (Beckacite K 5 parts by weight of polystyrene, 2 parts by weight of carbon black and 1 part by weight of Pigment Black. These materials are melted together and the melt, after being cooled, is ground and screened. 5 par-ts by weight of this toner, of a grain size of 10-30,IL, are mixed with 6 parts by weight of 4-chloro-1-naphthol, also of a grain size of about 10 to 30 The first blackcolored toner acquires a positive charge and adheres to the portions not struck by light; 4-chloro-1-naphthol acquires a negative charge, is repelled by the negatively charged image and settles on the margins of the image. 4-chloro-l-naphthol is dissolved away by treatment with alkaline liquids during the conversion of the image and an image very rich in contrast is obtained. A mixture consisting of 2% trisodium phosphate, 5% sodium metasilicate and 1% sodium hexametaphosphate in water is suitable as the alkaline solution for the preparation of the printing surface. After development, the printing plate is rinsed down with Water and inked up with greasy ink.

Example 7 The procedure described in Example 1 is followed, but for the development of the electrostatic image, two toners of the following composition are used:

(a) 10 parts by weight of polyvinyl carbazole are melted with 20 parts by weight of coumarone resin, 3 parts by weight of carbon black, and 2 parts by weight of spirit-soluble Nigrosine. When the melt has cooled, it is ground and screened.

(b) 10 parts by weight of adipic acid are melted with 2 parts by Weight of copper phthalocyanine and this melt too, when cool, is ground and screened.

2 parts by wei ht of the fraction of a particle size of 10 to 20 of the first toner, are mixed with 10 parts by weight of the fraction of a particle size of 10 to 20 of the second toner, and the mixture is scattered over the latent electrostatic image. The first, positively charged toner settles on the negatively charged image and the second, negatively charged toner on the parts that have been struck by light. After being heated to C, the image is converted into a printing surface. It is wiped over with a solution consisting of 1 part by volume of ammonia solution (25%) and 9 parts by volume of polyethylene glycol. It is then rinsed with water; dilute aqueous phosphoric acid is rubbed in and inking up with greasy ink is performed. Printing can now be effected in an offset machine.

Example 8 1 part by weight of a phthalic acid ester resin free of fatty acid, with a softening point of 7590 C. and an acid number of 85-100, and 1 part by weight of 2,5-bis- (4'-diethylaminophenyl-(1) )-1,3,4-oxadiazole are dis solved in 30 parts by volume of ethylene glycol monomethylether. This solution is coated upon an aluminum foil, roughened by brushing, and dried. By means of the electrocopying material prepared in this Way, an electrostatic image is produced as described in Example 1. This image is developed with a developer consisting of 5 parts by weight of anthracene-l-sulfanilide, 2 parts by weight of resorcinol and 1 part by weight of the toner described under (b) in Example 1. Anthracene-l-sulfanilide and .resorcinol acquire a negative charge and are repelled from the negatively charged image portions, but they adhere to the non-charged portions which have been struck by light. As they are alkali-soluble they are dissolved away during the preparation of the printing surface. The other toner, which is positively charged, adheres to the unexposed portions which are negatively charged. For conversion to a printing surface, the image is wiped over with a very dilute aqueous sodium hydroxide solution (about 0.5% rinsed briefly with water, treated with dilute aqueous phosphoric acid (about 2%), and inked up in the usual way with greasy ink.

Example 9 3 parts by weight of 2,5-bis-(4'-di-n-propylaminophenyl-(1'))-1,3,4-triazole and 0.005 part by weight of Acid Violet 6 EN are dissolved in 45 parts by volume of ethyleneglycol monomethylether. This solution is coated upon an electrolytically roughened aluminum foil and dried. With the electrocopying material prepared in this manner, electrocopies are prepared as described in Example 1. The electrostatic image is developed with a developer consisting of the following:

(a) A toner obtained from 10 parts by weight of polystyrene and 20 parts by weight of a ketone resin, with a melting point of 7682 C. and an acid number of (Kunstharz AP), 1 part by weight of carbon black and 2 parts by weight of spirit-soluble Nigrosine. These materials are melted together and the melt, after being cooled, is pulverized and screened. A fraction consisting of particles of from 0 to 10;]. is particularly suitable. The powder softens at about 90 C.

(b) 6-nitro-2-methyl-benzimidazole or -nitro-2-methyl-benzimidazole of a melting point of 218-220 C. which has a particle size of about 1 to These two toners are mixed together in the proportions of 8:10 and scattered over the image surface. Toner (a) is positively charged and develops the direct image. Toner (b), consisting of 5- or 6-nitro-2-methylbenzimidazole, is negatively charged and settles on the non-charged portions at the margins of the letters. When the image is fixed by heating, the 5- or 6-nitro-2-methylbenzimidazole with its higher melting point prevents running of the letters. Images rich in contrast are obtained; screen dots and fine lines are very well reproduced. For conversion to a printing surface, the image is wiped over with 5% acetic acid, containing a small quantity of gum arabic, briefly rinsed down with water, and inked up with greasy ink.

Example 10 10 parts by weight of 2,5-bis-(4-diethylaminophenyl- '(1'))-1,3,4-triazole and 0.05 part by weight of Rhodamine B Extra are dissolved in 100 parts by volume of ethyleneglycol monomethylether. This solution is coated upon a foil consisting of bright, rolled aluminum that has been cleaned with trichloroethylene and the coating is dried. For the production of an electrostatic image, the coating is negatively charged by corona discharge and then exposed for 4 seconds to a 100-Watt filament lamp at a distance of 25 cm. The electrostatic image of the master thereby produced is dusted over with a. developer consisting of the following two toners:

(a) 5 parts by weight of the interpolymer mentioned in Example 1, and

(b) 5 parts by weight of 5 (or 6)-nitro-2-methylbenzimidazole.

The interpolymer is negatively charged and adheres to the portions struck by light. The 5 (or 6)-nitro-2-methylbenzimidazole is positively charged and adheres to the negatively charged, unexposed portions. The image is fixed by heating to 180 C, For conversion to a printing surface, the image is wiped over with an aqueous solution containing 5% phosphoric acid, 5% gum arabic and 10% methanol, briefly rinsed down with water and inked up with greasy ink.

Example 11 A paper having a zinc oxide coating as a photo-conductor is negatively charged by means of a 6000-volt corona discharge and exposed to light under a master. The electrostatic image formed is powdered over with a developer consisting of 5 parts of malonic acid and 5 parts by weight of a colored resin mixture. The colored resin mixture is prepared as follows: 2.5 parts by weight of a polystyrene, with a softening point of 87 C. and an acid number of 0, are melted with 2.2 parts by weight of a ketone resin (Kunstharz AW 2), a condensation product of cyclohexanone and methyl cyclohexanone, with a softening point of to 90 C. and an acid number which is practically 0, and 0.3 part by weight of carbon black. When the melt has cooled, it is ground and screened. Toner particles of particle sizes less than 10g are particularly suitable for the reproduction of screen images. The toner particles of the malonic acid are negatively charged and adhere to the exposed parts while the colored toner develops the negative electrostatic image. When the image is fixed by heating, the malonic acid decomposes to form volatile products so that only the black-pigmented powder image is left.

Example 12 A mechanically roughened aluminum foil is coated with a mixture consisting of 400 parts by volume of ethylene-glycol monomethylether, 22 parts by weight of 2,4- bis-(4'-diethylarninophenyl-(1))-1,3,4 oxadiazole, 22 parts by weight of a styrene-maleic anhydride copolymer, having a specific gravity of 1.26-1.28 and a decomposition range from 200 to 240 C., and 0.022 part by weight of Rhodamine B Extra. The coated foil is then dried. For the production of an image on the electrophotographic reproduction material thus obtained, the layer is negatively charged by means of a corona discharge and then exposed for 0.5 second under an original to the light of a watt incandescent lamp. The electrostatic image of the master thus obtained is subsequently treated with a mixture consisting of (a) 25 parts by weight of 2-naphthol-disulfonic acid-( 3,6) and 20 parts by weight of naphthalene trisulfonic acid-( 1,3,6), and (b) 20 parts by Weight of a toner prepared by melting together, grinding and screening 9 parts by weight of a low melting point polystyrene (Polystyrol LG), 9 parts by weight of a maleic resin (e.g., Hobimal P 59), 1.5 parts by weight of Nigrosine, 0.2 part by weight of Pigment-Tiefschwarz, and 0.3 part by weight of carbon black. Both toners have a particle size of about 10 Toner (9.) takes on a negative charge, toner (b) a positive charge during the mixing process. When the mixed developer powder is contacted with the electrostatic image, the black pigmented toner with the positive charge is attracted by the negatively charged image, while the mixture of the uncolored toners having a negative charge is repelled. It, therefore, adheres to the uncharged edges of the black image. The image, provided with the toner, is fixed by heating to about C. An image corresponding to the master used is thus obtained. For transformation into a printing plate, the image is wiped over with a solution consisting of 10% monoethanolamine, 5% sodium silicate, and 85% polyethylene glycol. This alkaline solution dissolves the image-free portions of the layer as Well as the naphtholand naphthalene sulfonic acids adhering to the edges of the image. After a brief rinsing with water, the image is inked with greasy ink and used for printing in an offset machine.

If the aluminum foil used in the present example is provided with a positive charge, .a reversed image is obtained by means of the developer described above. The black pigmented toner (b), with the positive charge, adheres to the areas struck by light during exposure, while the toner (a), carrying a negative charge, is attracted by those areas of the image which were not struck by light and thus have retained the positive charge. After fixing, the image may be transformed into a printing plate by means of the alkaline developer used above.

It is thus possible to produce, by a simple reversal of polarity, but with the same kind of layer and the same developer, images corresponding to the master as well as reversed images thereof.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. A substantially dry developer for use in electrophotographic processes, consisting essentially of at least one toner which in use acquires a positive charge and at least one which acquires a negative charge, the toners being of approximately equal particle size, and at least one of the toners being selected from the group consisting of water-soluble toners, alkali-soluble toners, acid-soluble toners, toners which upon decomposition by heating form only products which are soluble in one of the said media, and toners which upon decomposition by heating form only products which are completely in the gaseous phase, one of the toners being removable from a base material independently of other toners located thereon after development of an electrostatic image in an electrophotographic process.

2. A toner mixture according to claim 1 in which the toner capable of acquiring a charge of one polarity has a melting point higher than the toner capable of acquiring a charge of opposite polarity.

3. A toner mixture according to claim 1 in which one toner comprises an interpolymer of vinyl chloride and the other comprises a colored mixture of a polystyrene and a maleinate resin.

4. A toner mixture according to claim 1 in which one toner comprises 5-chloro-2-methyl-benzimidazole and the other comprises a colored mixture of polystyrene and colophony.

5. A toner mixture according to claim 1 in which one toner comprises benzidine and the other comprises a colored ketone resin.

6. A toner mixture according to claim 1 in which one toner comprises 4-amino-anisol-e-Z-sulfonic acid and the other comprises a colored interpolymer of vinyl chloride.

7. A toner mixture according to claim 1 in which one toner comprises a zinc resinate and the other comprises p-amino-benzoic acid.

8. A toner mixture according to claim 1 in which one toner comprises a colored mixture of a maleinate resin and polystyrene and the other comprises 4-chloro-lnaphthol.

9. A toner mixture according to claim 1 in which one toner comprises a colored mixture of polyvinyl carbazole and coumarone resin and the other comprises adipic acid.

10. A toner mixture according to claim 1 in which one toner comprises a mixture of anthracene-l-sulfanilide and resorcinol and the other comprises a colored mixture of polystyrene and a maleinate resin.

11. A toner mixture according to claim 1 in which one toner comprises a colored mixture of polystyrene and a ketone resin and the other comprises nitro-Z-methylbenzimidazolc.

12. A toner mixture according to claim 1 in which one toner comprises an interpolymer of vinyl chloride and the other comprises nitro-2-methyl-benzimidazole.

13. A toner mixture according to claim 1 in which one toner comprises malonic acid and the other comprises a colored resin mixture.

14. A toner mixture according to claim 1 in which one toner comprises a naphthalene sulfonic acid and the other comprises a colored resin mixture.

15. A toner mixture according to claim 1 in which the toner of positive polarity comprises an organic compound having a melting point less than about C.

16. A toner mixture according to claim 1 in which the toner of negative polarity is a metal resinate.

17. A process for the production of a printing plate which comprises exposing a charged, supported, photoconductive insulating layer to light under a master, contacting the resulting electrostatic image with a substantially dry developer consisting essentially of at least one toner which in use acquires a positive charge and at least one which acquires a negative charge, the toners being of approximately equal particle size, and at least one of the toners being selected from the group consisting of watersoluble toners, alkali-soluble toners, acid-soluble toners, toners which upon decomposition by heating form only products which are soluble in one of the said media, and toners which upon decomposition by heating form only products which are completely in the gaseous phase fixing the developed image by a treatment selected from the group consisting of heating and contact with solvent vapors, and treating the surface of the plate with a liquid developer to form a relief image.

18. A process according to claim 17 in which the toner capable of acquiring a charge of one polarity has a melting point higher than the toner capable of acquiring a charge of opposite polarity.

19. A process according to claim 17 in Which one toner comprises an interpolymer of vinyl chloride and the other comprises a colored mixture of a polystyrene and a maleinate resin.

20. A process according to claim 17 in which one toner comprises 5-chloro-Z-methyl-benzimidazole and the other comprises a colored mixture of polystyrene and colophony.

21. A process according to claim 17 in which one toner comprises benzidine and the other comprises a colored ketone resin.

22. A process according to claim 17 in which one toner comprises 4-amino-anisole-2-sulfonic acid and the other comprises a colored interpolymer of vinyl chloride.

23. A process according to claim 17 in which one toner comprises a zinc resinate and the other comprises pamino-benzoic acid.

24. A process according to claim 17 in which one toner comprises a colored mixture of a maleinate resin and polystyrene and the other comprises 4-chloro-l-naphthol.

25. A process according to claim 17 in which one toner comprises a colored mixture of polyvinyl carbazole and coumarone resin and the other comprises adipic acid.

26. A process according to claim 17 in which one toner comprises a mixture of anthracene-l-sulfanilide and resorcinol and the other comprises a colored mixture of polystyrene and a maleinate resin.

27. A process acording to claim 17 in which one toner comprises a colored mixture of polystyrene and a ketone resin and the other comprises nitro-2-methyl-benzimidazole.

28. A process according to claim 17 in which one toner comprises an interpolymer of vinyl chloride and the other comprises nitro-Z-methyl-benzimidazole.

29. A process according to claim 17 in which one toner comprises malonic acid and the other comprises a colored resin mixture.

30. A process according to claim 17 in which one toner comprises a naphthalene sulfonic acid and the other comprises a colored resin mixture.

31. A process according to claim 17 in which the toner of positive polarity comprises an organic compound having a melting point less than about 150 C.

'15 32. A process according to claim 17 in which the toner 2,919,247 of negative polarity is a metal resinate. 2,965,573 3,010,842 References Cited by the Examiner 3,013,390 UNITED STATES PATENTS 5 3,078,231

2,638,416 5/1952 Walkup et al. 252-62.1 2,735,785 2/1956 Greig 25262.l 2,917,460 12/1959 Solar 25262.1

Allen 252- 62.1

Gundlach 25262.1 Ricker 25262.1 Bixby 117--17.5 Metcalfe et al. 25262.1

NOMAN G. TORCHIN, Primary Examiner.

PHILIP E. MANGAN, Examiner. 

17. A PROCESS FOR THE PRODUCTION OF A PRINTING PLATE WHICH COMPRISES EXPOSING A CHARGED, SUPPORTED, PHOTOCONDUCTIVE INSULATING LAYER TO LIGHT UNDER A MASTER, CONTACTING THE RESULTING ELECTROSTATIC IMAGE WITH A SUBSTANTIALLY DRY DEVELOPER CONSISTING ESSENTIALLY OF AT LEAST ONE TONER WHICH IN USE ACQUIRES A POSITIVE CHARGE AND AT LEAST ONE WHICH ACQUIRES A NEGATIVE CHARGE, THE TONERS BEING OF APPROXIMATELY EQUAL PARTICLE SIZE, AND AT LEAST ONE OF THE TONERS BEING SELECTED FROM THE GROUP CONSISTING OF WATERSOLUBLE TONERS, ALKALI-SOLUBLE TONERS, ACID-SOLUBLE TONERS, TONERS WHICH UPON DECOMPOSITION BY HEATING FORM ONLY PRODUCTS WHICH ARE SOLUBLE IN ONE OF THE SAID MEDIA, AND TONERS WHICH UPON DECOMPOSITION BY HEATING FORM ONLY PRODUCTS WHICH ARE COMPLETELY IN THE GASEOUS PHASE FIXING THE DEVELOPED IMAGE BY A TREATMENT SELECTED FROM THE GROUP CONSISTING OF HEATING AND CONTACT WITH SOLVENT VAPORS, AND TREATING THE SURFACE OF THE PLATE WITH A LIQUID DEVELOPER TO FORM A RELIEF IMAGE. 